When atomizing plant protectants with low discharge rates, lubricant oils and other substances which because of their toxicity may endanger the environment, it is necessary to prevent drifts into areas not to be sprayed. The danger of the atomized liquid drifting inherently increases the smaller the drop size. When atomizing liquids in the above applications, it is necessary therefore to achieve a fairly coarse drop spectrum. On the other hand uniform spraying of the intended areas demands as uniform a liquid distribution as possible.
The insight of the present state of the art is that the drop spectrum generated by a flat-jet nozzle shall be the finer the smaller the nozzle and hence the discharge rate. This means that when atomizing small amounts of ecologically stressful substances, the danger of small drops drifting will be real. As already indicated, such undesired drifting practically takes place foremost when highly concentrated plant protectants are discharged, and in particular when applying lubricant oils.
A further relation exists in that the drop spectrum of a single nozzle becomes finer as the pressure increases. Accordingly if the drop sizes are to be increased, the lowest pressure and the largest nozzle should be selected. While it is possible in this manner to achieve--to some extent--a coarse drop spectrum, there is failure on the other hand to meet the equally important requirement of uniform liquid distribution.
The U.S. Pat. No. 3,858,812 discloses a flat-jet nozzle of the initially cited kind and designed for low pressures. This known nozzle comprises a stepped liquid-guide means (borehole) which however assumes an oval shape at the liquid intake in order to affect the liquid distribution. In one embodiment mode this feature is implemented by means of a pane with oval borehole pressed into the nozzle. The purpose of this intake geometry is to correct a liquid distribution with excess emphasis on the edges. The large axis of the borehole oval is perpendicular to the large axis of the discharge slit, whereby the liquid is forced away from the edges and is more concentrated toward the center.
The oval borehole in the pane-like inset of the known nozzle lacks a throttling effect on the volumetric flow, at least it is not explicitly intended. As a result, the known features of U.S. Pat. No. 3,858,812 do not allow significantly controlling the drop spectrum in the sense of the desired increase in drop size.